This invention is directed towards the detection of stacking faults found on wafers by using a laser inspection system.
During wafer manufacturing and processing, defects can be deposited on the wafers which in turn may cause the device, that is to be fabricated on the wafer, to malfunction. In order to find these defects, several laser inspection tools have been developed. These tools have the ability to scan bare silicon wafers and measure the amount of scattered light, relative to the background level, coming from the laser hitting the wafer. The scattered light is then processed and it is determined whether or not the laser has hit a defect or not. This processing can tell the size and location of a particular defect.
Many of these laser inspection tools and systems do not accurately detect the various defects that occur on silicon wafers and during the manufacturing process. As the feature size of manufactured products decrease, every defect becomes important as even the tiniest defect can cause failures in the device being manufactured on the wafer. Therefore, it becomes increasingly necessary to obtain an accurate and precise detection of these defects.
Accordingly, the present invention provides systems and methods for improving the detection of defects found on wafers and particularly mound defects found on bare silicon wafers. Since defects can be various shapes, sizes and chemically different, the light scattering off the defect can vary depending upon the different defects on the wafer. Because many defects of similar type are oriented in the same direction on the wafer, the angle at which the wafer is scanned can maximize the light scatter that is collected by the collection optics of the surface scanning inspection system (SSIS).
In a preferred embodiment of the present invention it is necessary to obtain a high accurate count of stacking fault defects that are found on bare silicon wafers. An example of one type of stacking fault defect is mound defects. Mound defects are defined as light point defects (LPD) reported by the Tencor SS6200 laser particle measurement device, that are greater than 20.2 xcexcm in diameter, latex sphere equivalent (LSE). When the wafers are pre-aligned so that the wafer is rotated 45 degrees from the notch on the wafer and relative to the laser scan path, it is possible to get close to 100 percent, if not a 100 percent, capture rate for all stacking fault defects located on the silicon wafer. Therefore, the amount of defects located on each wafer is known. Thus, improved measurement capability of both the location and density of stacking fault defects provides a more accurate measurement of wafer quality.